The invention pertains generally to coiled tubing reels used in conjunction with coiled tubing injectors for performing well servicing and coiled tubing drilling operations.
Continuous pipe, generally known within the industry as coiled tubing since it is stored on a large reel, has been used for many years. It is much faster to run into and out of a well bore than conventional jointed straight pipe since there is no need to join or disconnect short segments of straight pipe.
Coiled tubing xe2x80x9cinjectorsxe2x80x9d are machines that are used to run continuous strings of pipe into and out of well bores. The injector is normally mounted to an elevated platform above a wellhead or is mounted directly on top of a wellhead. A typical coiled tubing injector has two contiguous chains. The chains are mounted on sprockets to form two elongated loops that counter rotate. The chains are placed next to each other in an opposing fashion. Tubing is fed between the chains. Grippers carried by each chain come together on opposite sides of the pipe and are pressed against it. The injector thereby continuously grips a length of the tubing as it is being moved in and out of the well bore. Examples of coiled tubing injectors include those shown and described in U.S. Pat. No. 5,309,900.
A coiled tubing reel assembly includes a stand for supporting a spool on which tubing is stored, a drive system for rotating the reel and creating back-tension during operation of the reel, and a xe2x80x9clevel windingxe2x80x9d system that guides the tubing as it is being unwound from and wound onto the spool. The level winding system moves the tubing laterally across the reel so that the tubing is laid across the reel in a neat and organized fashion. The coiled tubing reel assembly must rotate the spool to feed tubing to and from the injector and well bore. The tubing reel assembly must also tension the tubing by always pulling against the injector during normal operation. The injector must pull against the tension to take the tubing from the tubing reel, and the reel must have sufficient pulling force and speed to keep up with the injector and maintain tension on the tubing as the tubing is being pulled out of the well bore by the injector. The tension on the tubing must always be maintained. The tension must also be sufficient to wind properly the tubing on the spool and to keep the tubing wound on the spool. Consequently, a coiled tubing reel assembly is subject to substantial forces and loads.
Tubing reel assemblies are typically transported to wells with the required coiled tubing wound on the spool, and the spool installed in the reel assembly. Such spools are specially designed for the particular reel assembly and not meant to be disconnected or removed from the reel assembly during normal operation. A second reel assembly would therefore also have to be sent if there was need for a different diameter tubing or in the event that replacement tubing was required. Alternately, if replacement tubing was required, a shipping spool could be used to transport replacement tubing to the well. A lightweight spooling stand would then have to be used to support the shipping spool to transfer the tubing onto the spool of the working reel assembly. To save weight and size, these shipping spools do not possess the structure necessary to handle the loads typically imposed on reels during coiled tubing operations. Rather, shipping spools are designed as a relatively inexpensive means of transporting the tubing from a factory to a well. Therefore, transferring tubing from the shipping spool to the working reel assembly is necessary.
Transferring tubing from a shipping spool to a working reel induces extra strain in the tubing as it is unwound from the shipping spool then rewound onto the working spool. Since metal tubing is plastically deformed during spooling, transferring coiled tubing from a shipping spool to a working reel assembly reduces the life or number of hours that the tubing can be used, thus increasing the cost of coiled tubing operations. Furthermore, transfers typically involve spooling 20,000 to 25,000 feet of tubing at rates of 100 to 200 feet per minute. Therefore, considerable time is required to complete a transfer.
There exist coiled tubing reel stands for receiving common and ordinary shipping spools for use as working reels. These tubing reel assemblies require inserting a shaft through the center of the spool, and inserting a pair of driving knobs, mounted to a drive plate on the stand, into the side of the spool to provide the connection for the drive system. As a consequence, this type of reel stand has several problems. First, the reel stand either has to be separable into two halves so that the sides of the stand can be moved laterally away from each other, or has to have the sides of the stand capable of being swung outwardly, in order to allow the shipping spool of tubing to be loaded on the stand. Second, the spool has to be carefully aligned with the drive system on the stand. Spools wound with tubing are very large and heavy, weighing 30,000 to 60,000 lbs. on average. They are cumbersome and difficult to maneuver. Consequently, aligning a spool and the drive system on a rocking ship or in high winds is a difficult task. Third, as previously mentioned, standard and ordinary shipping spools are not built to handle the substantial loads encountered by a typical working spool.
Many of these problems are addressed by using a working spool that is removably mounted to a stand. The spool is supported on a stand by a pair of axles. A drive coupling, which is preferably formed when the spool is lowered onto the stand, transmits rotational motion to the spool. However, such a spool and stand assembly can be subject to several problems, one of which is caused by the fact that fluid used in drilling and workover operations is supplied to the coiled tubing under very high pressure. Passing the fluid through a bore created in an axle stresses the axle and a hub or other structure to which the axle is connected. To solve this problem, coiled tubing on a removable spool is coupled to a fluid source by a fluid conduit that extends through a bore in the axle. Stress created by the fluid pressure is not transferred to the axle and the structure supporting the axle, thereby avoiding having to reinforce the structure to which the axle is connected.
It is preferred that a relatively short fluid conduit, which will be referred to as a pipe, is passed through a bore in one of the two axles to connect the coiled tubing on the spool to a fluid source. The pipe is withdrawn at least far enough to provide enough clearance to allow the spool to be loaded onto the stand, and then extended so that it extends across a coupling of the spool to the stand. A swivel joint is coupled to one of the pipe""s two ends. If one side of the swivel joint is coupled to the end of the pipe that is inside of the spool, the other side of the swivel joint is coupled to the coiled tubing, and the end of the pipe outside the stand is coupled to the fluid source. In this configuration, the pipe remains stationary with respect to the stand when the spool rotates. If the swivel joint is coupled to the end of the pipe outside the spool, the coiled tubing is coupled to the opposite end of the pipe and the fluid source is then coupled to the swivel joint opposite the pipe. The pipe rotates with the spool when the swivel joint is mounted outside the spool. If desired, the swivel joint may be permitted to be attached at either end of the pipe, giving the option of having the swivel joint placed either inside the spool or outside the stand.